From PCT application WO 84/04822, a fused-fiber optical coupler is known which consists of two single-mode fibers welded together in parallel along a length in the centimeter range and drawn [pulled] to thereby form a coupler. The coupling region and the associated stripped fibers are placed in a housing. The fiber ends of the coupler are then spliced to a fiber of the communication line or to another electro-optic converter, for which reason the free ends of the coupler must be relatively long.
If such a coupler made of single-mode fibers is spliced to polarization-maintaining fibers, one of the optical axes must lie in the coupling plane (and the other must be perpendicular to the coupling plane), so that the degree of polarization (extinction) of the polarized light is retained. For this, the coupler fibers must be as short as possible to prevent depolarization of the light. This is very difficult to accomplish with the known coupler.